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From: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Newsgroups: comp.lang.perl
Subject: Re: Novice Question, Successive Lines
Keywords: Novice Question, Successive Lines
Message-ID: <7500@jpl-devvax.JPL.NASA.GOV>
Date: 21 Mar 90 19:50:56 GMT
References: <13447@cgl.ucsf.EDU>
Reply-To: lwall@jpl-devvax.JPL.NASA.GOV (Larry Wall)
Distribution: na
Organization: Jet Propulsion Laboratory, Pasadena, CA
Lines: 36

In article <13447@cgl.ucsf.EDU> alonso@maxwell.mmwb.ucsf.edu (Darwin Alonso) writes:
: How would one get perl to replace two or more successive blank lines 
: with one blank line?

Two primary ways.  First is the slurp method:

    undef $/;
    $_ = <>;
    s/\n{3,}/\n\n/g;
    print;

Second (and probably fastest) is the line-by-line method

    while (<>) {
	if ($_ eq "\n") {
	    while (<>) {
		last unless $_ eq "\n";
	    }
	    print "\n";
	}
	print;
    }

Alternately, there's

    while (<>) {
	next if "$prv$_" eq "\n\n";
	$prv = $_;
	print;
    }

There's also the grep method for Randal:

    print grep(($_ ne "\n" ? $_ : $prv eq "\n" ? '' : "\n", $prv = $_)[0], <>);

Larry